For an uplink channel of LTE-Advanced, which is an evolved version of 3rd generation partnership project long-term evolution (3GPP LTE), using both contiguous frequency transmission and non-contiguous frequency transmission is under consideration (see Non-Patent Literature 1). That is, in communication from each radio communication terminal apparatus (hereinafter referred to as “terminal”) to a radio communication base station apparatus (hereinafter referred to as “base station”), contiguous frequency transmission and non-contiguous frequency transmission are switched.
Contiguous frequency transmission is a method of transmitting a data signal and a reference signal (RS) by allocating such signals to contiguous frequency bands. For example, as shown in FIG. 1, in contiguous frequency transmission, a data signal and a reference signal are allocated to contiguous transmission bands. In contiguous frequency transmission, a base station allocates contiguous frequency bands to each terminal based on the reception quality per frequency band for each terminal, so that it is possible to obtain frequency scheduling effects.
On the other hand, non-contiguous frequency transmission is a method of transmitting a data signal and a reference signal by allocating such signals to non-contiguous frequency bands, which are dispersed in a wide range of band. For example, as shown in FIG. 2, in non-contiguous frequency transmission, it is possible to allocate a data signal and a reference signal to transmission bands which are dispersed all over the frequency band. In non-contiguous frequency transmission, compared to contiguous frequency transmission, the flexibility of assignment of a data signal and a reference signal to frequency bands is improved, so that it is possible to gain greater frequency scheduling effects. Further, in non-contiguous frequency transmission, it is possible to decrease the probability that all of a data signal or a reference signal of a terminal will get in a valley in fading. That is, according to non-contiguous transmission, it is possible to obtain frequency diversity effects and suppress deterioration of reception characteristics.
Further, in LTE, as shown in FIGS. 1 and 2, a terminal transmits a data signal and a reference signal in the same transmission band (see Non-Patent Literature 2). Then, a base station estimates a channel estimation value of the transmission band to which a data signal of each terminal is allocated, using a reference signal, and demodulates the data signal using the channel estimation value.
Further, in LTE, as a reference signal to use for propagation path estimation of an uplink channel, an orthogonal code called a cyclic shift sequence, which has high interference suppression effects, is employed (see Non-Patent Literature 3). Because one code sequence (ZC sequence) allocated to each base station (cell) is cyclically shifted by a different amount of cyclic shift, it is possible to obtain a plurality of cyclic shift sequences which are orthogonal to each other. An amount of shifting between cyclic shift sequences is set greater than delay time in a multipath channel. As shown in FIG. 3, a terminal transmits a cyclic shift sequence generated using a different amount of cyclic shift per terminal or antenna. A base station obtains a correlation value corresponding to each cyclic shift sequence by receiving a plurality of cyclic shift sequences that are multiplexed in a channel and performing a correlation calculation on a received signal and a base code sequence. That is, as shown in FIG. 4, the correlation value corresponding to cyclic shift sequence (CS #2) appears at the position which is shifted by cyclic shift width Δ from the position at which the correlation value corresponding to cyclic shift sequence (CS #1) appears. By setting cyclic shift width Δ greater than delay time in a multipath channel, it is possible to extract a correlation value in the period (detection window) in which an incoming wave of the desired wave exists.
Here, as a method of transmitting a reference signal in non-contiguous frequency transmission, two methods are possible. First, in transmission method (a) in FIG. 5, reference signals are generated from one code sequence. That is, transmission is performed by dividing one code sequence by a width corresponding to the bandwidth of each contiguous frequency band (hereinafter referred to as “cluster”), and allocating the obtained subsequence to each cluster.
On the other hand, in transmission method (b) in FIG. 6, reference signals are generated from a plurality of code sequences. That is, transmission is performed by generating a plurality of code sequences corresponding to the bandwidth of each cluster, and allocating each code sequence to clusters.